You were on the verge of death, your eyes barely open as you see a girl dressed in a school uniform, the girl utters some words, but you can't hear them as your eyes close

The Next Morning, you wake up confused, but decide to shrug it off as a dream

However, when you get to school, Rias Gremory personally invites you to The Occult Research Club, where she tells you that you are now a Devil, serving herself